Taxane derivatives represented by the following Chemical Formula (I) are known as anti-cancer agents having a broad spectrum of anti-cancer effects. Among such taxane derivatives, paclitaxel or docetaxel is generally known to those skilled in the art.

In the above formula, where R1 is acetyl and R3 is benzoyl, the compound is paclitaxel, and where R1 is hydrogen and R3 is tert-butoxycarbonyl (Boc), the compound is docetaxel.
Paclitaxel, one of the taxane derivatives, is a natural substance. Thus, it can be obtained by extraction from a yew tree, or by culturing yew tree cells, followed by separation and purification. Otherwise, it can be obtained from a semi-synthesis process comprising: collecting precursors, such as baccatin III or 10-deacetyl-baccatin III, present in a relatively large amount in leaves and stems of a yew tree; and converting the precursors into paclitaxel via chemical reaction. On the other hand, docetaxel is a non-naturally occurring synthetic substance. Thus, it is obtained by a synthetic process from a suitable precursor. Like paclitaxel, docetaxel is often obtained from a semi-synthesis process using precursors, such as baccatin III or 10-deacetyl-baccatin III.
Since the taxane-based compounds were known to have excellent anti-cancer activities, many semi-synthesis processes have been developed to date in order to produce various taxane derivatives, such as paclitaxel and docetaxel.
For example, a method for preparing 10-deacetyl-baccatin III derivative (docetaxel), including carrying out condensation of an oxazolidine compound as a side chain with hydroxyl-protected 10-deacetyl-baccatin III, is known (A. Commercon et al., Tetrahedron Letters, Vol. 33, 5185-5188, 1992). However, as shown in the following reaction scheme, the method requires additional reactions, comprising converting the side chain into a cyclized oxazoline derivative, and introducing a suitable substituent to the amine group of a side chain after the condensation.

In addition, International Patent Publication No. WO93/06094 (Holton et al.) discloses a method for preparing a baccatin III derivative (paclitaxel) by carrying out condensation of a protected beta-lactam compound as a side chain with hydroxyl-protected 10-deacetyl-baccatin III. The method is useful one including a simple process. However, it requires preparation of a specific protected beta-lactam compound. Further, the condensation should be carried out at a low temperature of −45° C. or lower under an anhydrous condition, as shown in the following reaction scheme.

Meanwhile, U.S. Pat. No. 4,924,011 (Dennis, et al.) discloses a method for preparing a 10-deacetyl-baccatin III derivative (docetaxel) by carrying out condensation of a protected acid as a side chain with a hydroxyl-protected 10-deacetyl-baccatin III under a mild condition. However, the method inevitably produces epimers (60:40) in the process of condensation, resulting in a significant drop in yield. In addition, the 10-deacetyl-baccatin III derivative obtained after removing the protective group is present in the form of a mixture with its epimer that should be removed to a very low degree due to its cytotoxicity. However, since the physico-chemical properties of the epimer are similar to those of the derivative, there is a difficulty in separating the epimer from the mixture in an industrial scale.